Warped carb base

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Jumprun
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Warped carb base

Post by Jumprun » Tue Jul 01, 2014 11:26 pm

I decided to remove my Carbs for some restorative work, right away I checked the bases and they are warped, I've only checked the first one and it will take a .024 feeler gauge when a straight edge is applied. I know I can put it on mill and spank it but it seems like a lot to take off. Has anyone ever gently straightened the base before machining to minimize the amount of material to remove? I have a good press and I'm not lame but I'm reluctant to go forward with this idea without hearing from the experienced.

Tom In SoCal

Colin Angell
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Re: Warped carb base

Post by Colin Angell » Wed Jul 02, 2014 7:00 am

Hi Tom

I would advise against trying to straighten the castings as you are likely to do more harm than good. The bases are simple to machine flat, either with a milling machine or just by sanding. Even with a relatively large gap the material is soft and will easily sand down on some good quality paper fixed to a flat plate. I work in an industry which uses wide machine sanders and I collect offcuts from abrasive paper rolls about 4 foot wide. Fixed down on a flat steel plate you can really push down hard and get a sensible cut and I have flattened large castings in this way, including timing chain covers. One advantage of using this method, for carburettors , rather than milling, is that the bodies don't get full of swarf.
Good Luck
Colin

Jumprun
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Re: Warped carb base

Post by Jumprun » Wed Jul 02, 2014 9:50 am

Hi Collin, thanks for the reply, what harm are you thinking of? Breaking a flange off? Are the castings that brittle? I'm thinking to straighten out about half of the warp and finish mill the remainder. I dreamed up a fixture that would consist of two thick pieces of steel, say 1.5 inches thick, machine them flat then drill through and tap for 4 fine thread studs to mount the carb base, then sandwich the base between said plates and evenly draw them together with 4 nuts. I suppose I could also forego the 4 studs and put the sandwich under a hand pump press.I figure if they can be warped so easily in use then they should be just as easy to move back a little.

The thing I don't like about machining the entire .025" is that it will thin the flange, making them even more prone to warping.

Timo
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Re: Warped carb base

Post by Timo » Wed Jul 02, 2014 10:07 am

I would highly advise AGAINST milling or sanding the bottoms of the carburetor. In todays world these methods should be considered only as a last resort or in case of a emergency if your stuck in the middle of antarctic, desert or jungle with other way out or ability to contact outside world. There's an excellent service provided by Pierce Manifolds in Gilroy, California where they have experience and tooling to straighten (and restore) Weber carburetor bases, bodies and tops, etc.
if one stops and thinks about it for more than a second, by milling or sanding the base can be made straight, but the rest of the body will remain distorted and if this method is repeated over the years (or decades) after inevitably continued warpage over time and usage, the further distorted bodies, throttle plate or throttle shaft bores can not be brought back to "square" without major metallurgical "surgery" (read expense). I have no vested interest in aforementioned business other than that they have and will continue provide carburetor service for me and my client vehicles equipped with older Webers.
There might be other companies providing similar service, but I have no knowledge of them.
Timo

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Tom Wilson
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Re: Warped carb base

Post by Tom Wilson » Wed Jul 02, 2014 12:15 pm

My carbs are currently at Pierce Manifolds and have warped bottoms as well. I am no expert at this, but after touring the shop and seeing what they do, I knew I was out of my league and let them do the work.

Mike Pierce tells me he gets a lot of carbs where people tried to bend the tabs back straight and snap them right off. The material used in these carbs (36DCS') is quite brittle and bending them one way causes them to be even more brittle when you bend them back. Mike's crew puts them in an oven and over the course of a week, using a constantly changing set of shims, bends each one back individually. It is not easy, but they do not break.

After the bottoms of my carbs were straightened, we rechecked the bores and they were warped as well, though not as bad as when the process started. Because they are warped, the throttle plates cannot close properly and leak. In mine, they actually cut a ridge into the walls of the bore from banging against it. It takes very careful alignment to bore these out properly, one I would not try at home. There is one point in the lower section of the bores where the walls are very thin and a lot of measuring has to be done to make sure that you take enough away to straighten things out without breaking through. If you do break through, then you are talking big bucks. Note that because I now have slightly bigger bores, we need slightly bigger throttle plates, but at least they will be round.

Also note that your throttle shafts are probably worn. Mike says the shafts wear very quickly and when people hear the air leaking out of them, they assume it is coming from the bottom and tighten down the nuts that attach the carb to the engine. This tightening warps the entire carb, which pinches on the shaft and stops the leaking noise for a little while. Soon, however, the leaking starts again and we tighten down further, which is why our carbs end up all out of wack.

Send them out, get them done right and don't tighten them down too much!
Tom Wilson - Series III 250 GTE, SN 4247 GT
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Jumprun
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Re: Warped carb base

Post by Jumprun » Wed Jul 02, 2014 12:36 pm

Tom Wilson wrote:My carbs are currently at Pierce Manifolds and have warped bottoms as well. I am no expert at this, but after touring the shop and seeing what they do, I knew I was out of my league and let them do the work.

Mike Pierce tells me he gets a lot of carbs where people tried to bend the tabs back straight and snap them right off. The material used in these carbs (36DCS') is quite brittle and bending them one way causes them to be even more brittle when you bend them back. Mike's crew puts them in an oven and over the course of a week, using a constantly changing set of shims, bends each one back individually. It is not easy, but they do not break.

After the bottoms of my carbs were straightened, we rechecked the bores and they were warped as well, though not as bad as when the process started. Because they are warped, the throttle plates cannot close properly and leak. In mine, they actually cut a ridge into the walls of the bore from banging against it. It takes very careful alignment to bore these out properly, one I would not try at home. There is one point in the lower section of the bores where the walls are very thin and a lot of measuring has to be done to make sure that you take enough away to straighten things out without breaking through. If you do break through, then you are talking big bucks. Note that because I now have slightly bigger bores, we need slightly bigger throttle plates, but at least they will be round.

Also note that your throttle shafts are probably worn. Mike says the shafts wear very quickly and when people hear the air leaking out of them, they assume it is coming from the bottom and tighten down the nuts that attach the carb to the engine. This tightening warps the entire carb, which pinches on the shaft and stops the leaking noise for a little while. Soon, however, the leaking starts again and we tighten down further, which is why our carbs end up all out of wack.

Send them out, get them done right and don't tighten them down too much!
Excellent experienced reply, just what I was looking for thanks Tom and others. Ok I guess I'll be calling Pierce, I can see I need an expert to work on them.

Jumprun
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Re: Warped carb base

Post by Jumprun » Wed Jul 02, 2014 3:14 pm

Ok, I talked to Mike at Pierce about my carbs, albeit expensive ones. Surprisingly enough the car was running quite well before I decided to inspect the carbs, but I'm glad I did before they got worse or caused me headaches down the road.

Ok now the bad news, the lead time is 10 weeks! but this will give me more time to get into further trouble while I wait.

Blue Skies from SoCal, Tom

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Tom Wilson
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Re: Warped carb base

Post by Tom Wilson » Wed Jul 02, 2014 4:31 pm

You have stepped into the Pebble Beach Vortex... Two months before the show every shop seems to slow way down and focus on the big boys who will pay extra to rush jobs through before August. Can't blame them, though and I am happy to pay downtime prices.
Tom Wilson - Series III 250 GTE, SN 4247 GT
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kare
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Re: Warped carb base

Post by kare » Thu Jul 03, 2014 3:55 am

Zinc alloy items (both DCZ and DCS were made of Zamac) snap right of if you try to bend them. The only way to cold work the material is sharp blows with a hammer as they send dislocation waves through the crystal boundaries and the geometry changes by each blow (I am a M. Sc. with training in metallurgy).

I understand that Mike Pierce has created exactly the right method of returning the carb bodies back to correct shape, so you should not under any circumstances try to do it at home!!!

Another warning: when you take your car out of storage and it runs like shit, you should NEVER start tightening the base or lid screws (or adjusting the carbs). Dried out paper gaskets leak air and it goes back to normal when the gas soaks them again. Many mechanics pic up a screw driver as a reflex when they hear an engine with out of tune Webers. I have seen hundreds of distorted carb lids as a result. Bottom line: NEVER TOUCH A CARB AFTER A CAR CAME OUT OF STORAGE. Even "Just a little" is WAY TOO MUCH!!!

Timo
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Re: Warped carb base

Post by Timo » Thu Jul 03, 2014 8:43 am

kare wrote:
I understand that Mike Pierce has created exactly the right method of returning the carb bodies back to correct shape, so you should not under any circumstances try to do it at home!!!

Another warning: when you take your car out of storage and it runs like shit, you should NEVER start tightening the base or lid screws (or adjusting the carbs). Dried out paper gaskets leak air and it goes back to normal when the gas soaks them again. Many mechanics pic up a screw driver as a reflex when they hear an engine with out of tune Webers. I have seen hundreds of distorted carb lids as a result. Bottom line: NEVER TOUCH A CARB AFTER A CAR CAME OUT OF STORAGE. Even "Just a little" is WAY TOO MUCH!!!
+ 1 and another reminder why it's NOT a good idea to have cars sit un-used for long periods of time, even if in climate controlled or otherwise supposedly ideal environment.
Timo

Jumprun
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Re: Warped carb base

Post by Jumprun » Thu Jul 03, 2014 5:39 pm

We all know the warped carb base syndrome is very common on carburetors that use fiber or phenolic spacer on the manifold (not just Ferrari) This warping occurs when the spacer compresses unevenly because it is a soft material.

Ok, now what? will people continue to warp carbs forever? or is there some different material we can use for the spacer, something that will prevent heat soak yet not yield to the forces of a wrench and heat? perhaps a Carbon fiber composite? It's easy to say "just don't tighten them as much" but wouldn't be nice to not worry while getting the bases to seal well too?

--Tom

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Re: Warped carb base

Post by Steve Meltzer » Thu Jul 03, 2014 6:13 pm

I second all that's been said. Tho' I've spent a lot of time foolin' with the Webers on my cars, I'm no expert. But I can tell you that Mike Pierce is the go to guy for this and he knows all about how to get them straight and flowing as good as they can. When the bores are out of round and the butterflies won't seal, or as noted, when the throttle shafts have "ovaled" their orifices, most of us just can't fix that and Mike does it with aplomb (or whatever he uses!). Really nice guy, extremely knowledgeable and friendly. You might have to wait for the Waltons and Lenos of the car world, but it's worth the wait, and he does his best to get the work done ASAP. Not cheap, but you can't replace these carbs. s
steve
meltzer, "“With a Ferrari, whatever it is, it’s a $1000. If that’s what it is.”"
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Colin Angell
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Re: Warped carb base

Post by Colin Angell » Fri Jul 04, 2014 5:39 am

Hi all

Gosh I have been surprised by some other replies on this, Tom Yang site. I thought most of us had dirt under our nails and actually drove the cars.

A most common failing with 40 to 50 year old Weber carburettors is that the bodies warp through a mixture of heat and being over tightened and the spindle bearings wear oval through use. Both of those faults lead to a loss of vacuum but both faults are quite easily addressed in a well equipped home shop. I haven't personally had much of a problem with ovality of the choke bores, but it would be interesting to find out what difference that actually makes to fuel flow, other than the throttle plate not sealing properly which affects slow running, but not much else. That could be resolved quite easily by filing the plates oval to match.

I would probably put money on that no one would be able to tell the difference when actually driving the cars even under very spirited conditions. I guess full race preparation you would be aiming for perfection, but I have no experience with racing.

Response awaited!

DWR46
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Re: Warped carb base

Post by DWR46 » Fri Jul 04, 2014 12:17 pm

Colin: Actually, it is the other way around. It is very easy to make a carburetor work in racing conditions, as you spend very little time on part throttle. You are either wide open or closed most of the time. The "ovaled" bores have the greatest effect on the progression period, as the throttle plates uncover the series of progression holes to make the engine run smoothly as the car is driven off from a standing start. "Ovaled" bores and loose throttle plates cause havoc on the fuel mixtures in these conditions. Most of these cars have had worn carbs for so long, that many of us just do not understand how well they can run with everything to new specs. We just get used to the quirky nature of the car and think that is "normal".

Timo
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Re: Warped carb base

Post by Timo » Fri Jul 04, 2014 12:50 pm

Hi Colin and all,

I know my replies/writing can appear somewhat harsh at times, perhaps due to not having any formal education in English language coupled with the fact that I'm and have been quite passionate vintage cars enthusiast/hobbyist for almost 40 years and professionally repairing/restoring/servicing them for almost 30. I'm always trying to do any/all work to best of my ability and continually trying to learn ways of doing things better.
These traits unfortunately have also created slight lack of tolerance for any attempts to get things done "on the cheap" or "just enough to get it going", especially when it comes to mechanical/operational aspects of our beloved objects. I personally believe any and all vintage cars deserve the respect of being done as right as possible and especially mechanically so it can actually be enjoyed as intended for what it is, a car. I do understand most of us, including myself, at times face financial restraints to provide a proper care/custodianship for them, but it would show more respect for a given vehicle if irreversible unorthodox repairs/services were not conducted due to just lack of proper funding.

Back to Webers and their bores. Like you Colin, I don't have much race experience, but if I understand correctly most of it is conducted off idle and in the range closer to full open throttle, in which case slight out-of-round bores may not make a huge difference. Road/street cars, on the other hand, often utilize idle circuit during common operations and idle circuit will be effected by slightest discrepancies, even more so in multiple carburetor (un-shared plenum) set ups found in older Ferrari vehicles.

And with all due respect, any attempt to "file" throttle plates is comparable to just tossing the carbs into trash bin before even starting.
These plates and most of the carburetor components are carefully engineered, PRECISION MACHINED items with specific angles and surface finishes to provide precise fit within their respective location and any detectable wear or discrepancy usually requires replacement or if replacement is not available, comprehensive understanding AND ability to appropriately correct them.
Timo

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